Slack is a great example. My first thought was Jira. It’s a great software for functionality, but it’s so unbelievably slow that I tend not to use it at all. We have a quite powerful server for Jira and just five users. It should work out fine, but I encountered waiting times of a minute to just load the start screen. It feels like running all the time and as soon as you need to do something in Jira you’re trapped in quicksand.